Polyethylene block-graft copolymers and method for preparing the same

ABSTRACT

The present invention provides a block-graft copolymer of polyethylene and saponified ethylene vinyl acetate with improved moisture permeability by heating a mixture of polyethylene and a saponified ethylene-vinyl acetate copolymer to an elevated temperature and kneading the mixture under pressure. The saponified ethylene-vinyl acetate copolymer has a degree of saponification of 99% or more and consists of from 30 to 50 mol percent of ethylene, the remainder being vinyl acetate, the polyethylene being a powdery high density polyethylene which has not been subjected to heating and kneading after polymerization, the mixture containing the high density polyethylene and the saponified ethylene-vinyl acetate copolymer at a weight ratio of 98:2 to 80:20 and from 0.2 to 0.6 percent by weight based on the weight of the mixture, of a radical forming catalyst, and the mixture being heated to a temperature of from 200* to 205*C and kneaded under a pressure of 330 to 470 kg/cm2.

United States Patent [191 Kishimoto et a1.

[ Jan. 29, 1974 POLYETHYLENE BLOCK-GRAFI COPOLYMERS AND METHOD FORPREPARING THE SAME [73] Assignee: Toyo Seikan Kaisha, Ltd., Tokyo,

Japan 22 Filed: Nov. 30, 1971 21 Appl.No.:203,252

Related US. Application Data [63] Continuation-impart of Ser. No.862,392, Sept. 30,

1969, abandoned.

[30] Foreign Application Priority Data 3,549,727 12/1970 Coates et a1.260/897 3,299,194 1/1967 Golike 260/897 3,399,250 8/1968 Kirk et a1260/897 Primary ExaminerMurray Tillman Assistant Examiner-C. J. SeccuroAttorney, Agent, or Firm-E. F. Wenderoth et a1.

[5 7] ABSTRACT The present invention provides a block-graft copolymer ofpolyethylene and saponified ethylene vinyl acetate with improvedmoisture permeability by heating a mixture of polyethylene and asaponified ethylenevinyl acetate copolymer to an elevated temperatureand kneading the mixture under pressure. The saponified ethylene-vinylacetate copolymer has a degree of saponification of 99% or more andconsists of from 30 to 50 mo] percent of ethylene, the remainder beingvinyl acetate, the polyethylene being a powdery high densitypolyethylene which has not been subjected to heating and kneading afterpolymerization, the mixture containing the high density polyethylene andthe saponified ethylene-vinyl acetate copolymer at a weight ratio of98:2 to 80:20 and from 0.2 to 0.6 percent by weight based on the weightof the mixture, of a radical forming catalyst, and the mixture beingheated to a temperature of from 200 to 205C and kneaded under a pressureof 330 to 470 kg/cm 3 Claims, 8 Drawing Figures PATENTEDJAHZQIQH3.789.085

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l l I r 5 6 7 a 9 1p POLYETHYLENE BLOCK-GRAFI COPOLYMERS AND METHOD FORPREPARING THE SAME CROSS-REFERENCE TO RELATED APPLICATIONS:

This application is a continuation-in-part patent application, of Ser.No. 862,392, filed on Sept. 30, l969, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to a polymer alloycomposed mainly of block-graft copolymers containing ethylene as theskeleton and a method of preparing the polymer alloys, and moreparticularly to a novel method of man ufacturing synthetic resins foruse in the art of moulding and having improved moisture permeability,organic liquid permeability, environmental stress cracking property,heat shrinkage and other various characteristics by heating and kneadinga mixture of powdery high density polyethylene resins which have beenpolymerized but not heated and kneaded and a saponified ethylene-vinylacetate copolymer, in the presence of a free radical forming catalyst orcompound.

Organic synthetic resins in the form of films, laminations, bottles,fibers or containers in the form of various configurations are nowwidely used to pack foodstuffs, toilet goods, medical supplies andvarious other commercial products. Especially, polyethylene,polystyrene, polyvinyl chloride and the like are widely used for thepreparation of packing films, bottles and other containers because theyhave excellent properties and can be readily produced at low cost onmass production basis. However, polyethylene, for example, is permeableto straight chain hydrocarbons, aromatic hydrocarbons, esters, ketonesand other organic solvents. Further, polystyrene and polyvinyl chlorideare permeable to above described organic liquids and inorganic liquidssuch as water, and in addition they manifest poor shockproofness,environmental stress cracking property and heat shrinking property. Toeliminate these defects of various resins it has been proposed to blendhomologous high molecular resins or to synthesize random copolymers frommonomers. However, mixtures and copolymers obtained by such methodsmerely show properties intermediate of respective properties ofrespective components so that it is impossible to radically improve thecharacteristics of the products. Commercially available granular orpulverized high density polyethylene resins which have been subjected toheating and kneading after polymerization generally lack compatibilitywith other type polymerized polyethylene resins so that improvement inthe quality by blending can not be expected. More recently, variousmethods have been developed wherein homologous block copolymers of thepolyester series or of polyamide series are synthesized by the esterexchange reaction or amide exchange reaction or wherein block copolymersor graft copolymers are synthesized from monomers. However, thesemethods are not suitable for practical use because of high cost ofmanufacturing involved.

Mixtures and graft copolymers of polyolefin and other polymers aredisclosed in US. Pat. Nos. 3,093,255 and 3,261,885. The former relatesto a blend of polyolefin and polyamide while the latter to a method ofpreparing a block-graft copolymer by kneading a mixture of a homopolymeror copolymer of olefin and styrene, and a linear polyamide having -NHCOradicals in the presence of a free radical forming catalyst.

As above described, in the methods disclosed in these patents, polymerswhich can be used with polyolefin are limited to highly reactivepolyamide. This invention is different from these prior art in that itis characterized by blending polyethylene resins with a saponifiedethylenevinyl acetate copolymer having low reactivity thereto in thepresence of a free radical forming catalyst. Further this invention isalso different from said prior patents in that polyethylene resins arelimited to powdery high density polyethylene resins which are not yetsubjected to heating and kneading after polymerization.

SUMMARY OF THE INVENTION It is an object of this invention to provide anovel block-graft copolymer and a novel method of manufacturingsynthetic resins for use in the art of moulding wherein a mixture ofpowdery high density polyethylene resins which are not yet subjected tosuch operations as heating and kneading after polymerization and asaponified ethylenevinyl acetate copolymer is heated and kneaded in thepresence of a radical forming catalyst. Containers moulded from thenovel resins manifest excellent moisture permeability, organic liquidpermeability, environmental stress cracking property and heat shinkproperty which are lower than those of respective raw material resins.Thus, for example, while the moisture permeability (measured by J IS Z0208) of high density polyethylene is about 5 g/m .day-50 p. and that ofpolystyrene resin is about 40 g/m 'day'50 [1,, the novelpolyethylene-polystyrene moulding resin shows a moisture permeabilityranging from 0.5 g/m 'day-50 p. to 3 g/m 'day-5O p. which is much lowerthan that of each component resin.

The term powdery high density polyethylene resins" utilized in thisspecification means homopolymers or copolymers which have a specificgravity of higher than 0.94 and prepared by polymerizing, under a lowpressure or a medium pressure, ethylene or a mixture of ethylene, themajor component, and other olefin monomer, such as butene, hexene,octene, propylene and which have not been subjected to any operationssuch as heating and kneading after polymerization. Although, resinshaving a melt index of less than 15.0 g/ 10 min. (ASTM, D] 238) areeffective resins having, a melt index of less than 1.0 g/l0 min. arepreferred. These resins are in the form of a powder and the pre ferredmean grain size is less than 2,000 t.

As above described, according to this invention, to a not kneadedpowdery high density polyethylene resin is added a saponifiedethylene-vinyl acetate copolymer at a weight ratio of 98 2 to 20. Thesaponified ethylene-vinyl acetate copolymer employed in this inventioncontains 30 50 mol percent of ethylene and has a degree ofsaponification of 99 percent or more and a melt viscosity of 170,000poise at a temperature of 1909C anglgndgr a rate of shear at 30 SCCF.

As the radical forming catalyst, there may be used azo compounds,peroxide, and the like. Examples of such catalysts are 2,2-azobisisobutyronitrile, benzoyl peroxide, benzoin peroxide,benzo-benzoyl peroxide, anthracene, chloroanthraquinone or the like.Concentration of the radical forming catalyst varies, dependent upon thetype of the substance formed. Concentration of from 0.005 to 10.0 parts,based upon 100 parts of the resin mixture, is effective butconcentration of less than 5.0 parts is preferred.

As the kneading device may be used a conventional screw type extruder,heated rolls, a Bumburys mixer or the like. Kneading conditions dependupon the type of saponified ethylene-vinyl acetate copolymers,especially their thermal characteristics as well as the types of theradical forming catalysts and kneading machines used. However, with heatkneading with the screw type extruder, resin pressure at the exit end ofthe screw of more than 100 kg/cm the temperature of the die ranging from155C to 290C and the number of revolutions of the screw ranging from 25to 45 rpm are preferred. 15 P Table 1 Samples A B C D E F G H l J Sample0.34 2.8 l 1.94 1.69 2.3 12.1 3.1 3.4 3.2 8.9

a Same resin but 0.18 8.0 l0 2.79 2.75 5.l 10" 17.6 6.6 8.0 1.7 4.3kneaded once Sample 0.36 2.1 X10 2.64 1.62 l.9 10 16.5 2.9 3.2 2.0 5.5

b Same resin but 0.33 3.2Xl0 2.57 1.70 2.0X10 16.8 2.1 5.4 1.9 5.0kneaded once A: melt index (g/lO min) B: apparent viscosity, at 190C,1.0 sec (poises) C: swelling ratio, at I90"C, 100 sec" D: intrinsicviscosity (100 ml/g) E: number average molecular weight F: molecularweight distribution (calculated from the weight average.

molecular weight and the number average molecular weight) G: gelfraction H: number of total methyl radicals (per 1000 carbon atoms) l:coefficient of light absorption of ethyl brunch"" J: coefficient oflight absorption of terminal vinyl radicals"" "z Obtained by infraredspectro-analysis.

When utilizing heated rolls in nitrogen atmosphere, roll temperatureranging from 150C to 230C, number of revolutions of rolls ranging fromto rpm and kneading time ranging from 5 to 15 minutes are preferred.When effecting heating and kneading by utilizing a Bumburys mixer, resintemperature of 130C to 230C, number of revolutions of the rotor of 15 torpm. and kneading time ranging from 3 to 8 minutes are preferred.Utilization of more effective kneading device results in the reductionof the kneading time. Although kneading temperature varies dependentupon the. type of the kneading device, melting point of the saponifiedethylene-vinyl acetate copolymer used and other factors, generallytemperatures 30C to 250C higher than the melting point of the powderyhigh density polyethylene resins are preferred.

When moulded by a conventional extruder or an injection mouldingmachine, the synthetic resin prepared as above described or a roomtemperature mixture thereof with a powdery high density polyethyleneresin which is not yet subjected to heating and kneading afterpolymerization gives moulded articles having low mois- As can be clearlynoted from table 1 changes in the melt index, apparent viscosity (at 1.0secf), swelling ratio (at sec."), intrinsic viscosity, number averagemolecular weight, molecular weight distribution M 17, gel fraction,number of total methyl radicals, number of ethyl radicals branched, andnumber of terminal vinyl radicals are more remarkable in the highdensity polyethylene resin not heat kneaded after polymerization thanthe same type resin which has been kneaded. From these results it can bepresumed that in the high density polyethylene resin, the first heatkneading operation after polymerization results in a high mechanical andchemical reactivity in the molecules causing above described changes inthe molecular characteristics. On the other hand, in the vinylpolymerization type resins heat kneading operation cratesmechano-chemical reactivity. As an example, changes in the meltviscosity (C, 30 sec.) and intrinsic viscosity (solvent: a mixture of 85percent by weight of phenol and 15 percent by weight of water,temperature: 30C) caused by kneading of a polyvinyl chloride having amean degree of polymerization of 800 are shown in table 2.

Table 2 Sample A B Saponified ethylene-vinyl 1.7 X 10 0.11 acetatecopolymer Same resin but kneaded 3.2 X 0.14

once

A: Apparent viscosity (poise) at 190C, and at a rate of shear of 30 sec.8: Intrinsic viscosity at 30C, solvent a mixture of 85 percent, byweight of phenol and percent, by weight of water.

The saponified ethylene-vinyl acetate copolymer was kneaded with anextruder having a screw, 40 mm diameter, and 1,120 mm long and rotatedat a speed of 45 rpm. The temperature of the die was 230C. Further theresult of analysis by the nuclear magnetic resonance method shows thatthe pattern of the resin prepared by this invention is similar to thoseof block copolymers regarding respective components and that thepercentage of solvent extraction of the novel synthetic resin is muchsmaller than that of the case wherein the high density polyethyleneresin heat kneaded after polymerization was blended. As shown in table 3below heats of fusion of respective crystals as determined by thedifferential thermal analysis technique is different from the syntheticresin prepared in accordance with this invention and for a compositionprepared by kneading a mixture of the same type pulverized high densitypolyethylene heat kneaded after polymerization and vinyl polymerizationtype resins.

acetate copolymer Powdery high density polyethylene resin not kneadedafter polymerization High density polyethylene resin kneaded afterpolymerization Melt index: 0.8 A: Heats of fusion (cal/g) of highdensity polyethylene crystals B: Heats of fusion (cal/g) of saponifiedethylenevinyl acetate copolymer From these results it can be thoughtthat heat kneading operation carried out in the presence of a radicalforming catalyst is effective to greatly activate unsaturated radicals,methyl radicals and other radicals contained in respective resins thusforming block copolymers of high density polyethylene resins andsaponified ethylene-vinyl acetate copolymer, or graft copolymers orcrosslin'ked polymers thereof represented by the general formula.

where A represents high density polyethylene resins and B saponifiedethylene-vinyl acetate copolymer. Thus, the product is not a mere blendbut it is considered that new substances are formed whose structure hasbeen chemically changed, and that such novel substances contribute tothe improvement of various characteristics, such as moisturepermeability and others described above.

The term moulded articles," herein used, is intended to cover articlesof any geometrical configuration, such as films, sheets, tubes, fibers,bottles and the like.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing:

FIG. 1 shows a NMR spectrogram of an ethylene propylene block copolymer;

FIG.2 shows a NMR spectrogram of a polyethylene polypropylene blend (amixture at room temperature);

FIG. 3 shows a NMR spectrogram of the same resin as in FIG. 2, butpolyethylene was subjected to heat kneading process;

FIG. 4 shows a NMR spectrogram of the novel polyethylene polypropyleneblock-graft copolymer (polyethylene: powdery high density polyethylene);

FIG. 5 shows a NMR spectrogram of a polyethylene polystyrene resin (amixture at room temperature);

FIG. 6 shows a NMR spectrogram of the novel polyethylene polystyreneblock-graft copolymer (polyethylenezpowdery high-density polyethylene);

FIG. 7 shows a NMR spectrogram of a polyethylene- PVC synthetic resin (amixture at room temperature) and FIG. 8 shows a NMR spectrogram of thenovel polyethylene polyvinyl chloride block-graft copolymer(polyethylene:powdery high-density polyethylene).

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following specific examplesare given by way of illustration, and are not to be considered aslimiting in any way the scope and spirit of the invention.

EXAMPLE I In order to determine whether chemical change occurs or not inthe structure when a mixture of a powdery high density polyethyleneresin not kneaded after polymerization and a vinyl polymerization typeresin is heat kneaded in the presence of a radical forming catalyst, apowdery high density polyethylene resin not kneaded after polymerizationand having a melt index of 0.6 (ASTM D-l238), and a melt viscosity of180,000 poise at a temperature of 190C and under a rate of shear at 30sec. (a homopolymer, but incorporated with 0.05 part of ionolanti-oxidant) and a propylene resin having a flow rate of 1.0, and amelt viscosity of 120,000 poise at a temperature of 190C and a rate ofshear at 30 sec. were admixed at room temperature and at a weight ratioof 20. As the radical forming catalyst, 0.10 part of 2,2-azobisisobutyronitrile was incorporated to the mixture and the resulting mixturewas subjected to heat kneading process which was conducted in a ventedextruder provided with a nylon type screw, 40 mm diameter and 1,120 mmeffective length. The conditions of heat kneading were: the temperatureof the resin at the die was 265C, the resin pressure at the dischargeend of the screw was 1 kg/cm and the number of revolutions of the screwwas 29 rpm.

For comparison, the same type high density polyethylene resin but onceheat kneaded after polymerization was admixed with the same typepolypropylene resin at a weight ratio of 80 .0. 10 part of 2,2-azobisisobutyronitrile was incorporated and the resulting mixture was heatkneaded with the same extruder under the same extrusion conditions.

An ethylene-propylene block copolymer was prepared by first polymerizingpropylene in a solvent in the presence of triethyl aluminum and titaniumtetrachloride and then effecting addition polymerization of ethylenemonomer to said living polymer, the ratio of ethylene propylene in thecopolymer composition being 79 21. NMR spectra were determined by meansof a nuclear magnetic resonance device operating at 60 MHz on threetypes of resins synthetized as above described and a room tempe aturemixture of the same type high density polyethylene but once kneadedafter polymerization and the same type polypropylene (at the weightratio of 80 20). Hydrogen protons were used as the nuclei, purifiedorthodichloro benzene as the solvent. Measuring temperature was 160C forall samples while the concentration of each sample was 6.0 percent. Allother measuring conditions were maintained constant. The NMR spectrumfor the ethylene-propylene block copolymer is shown in FIG. 1, that fora room temperature mixture of heat kneaded high density polyethylene andpolypropylene in FIG. 2, that for the mixture consisting of high densitypolyethylene once kneaded after polymerization and polypropylene, saidmixture being kneaded in an extruder, is shown in FIG. 3 and that forthe synthetic resin prepared according to this example in FIG. 4. Bycomparing FIGS. 1 and 2 it will be noted that signal intensitiesmanifested by the protons of methyl, methylene and methine (representedby a, b and c respectively in FIG. 1 to 4) radicals contained inpropylene of the ethylenepropylene block copolymer are less than thoseof the room temperature mixture. According to the result (shown in FIG.3) of the mixture prepared by admixing heat kneaded high densitypolyethylene and polypropylene and then kneading in an extruder, theintensity of each signal is substantially the same as that (FIG. 2) ofthe room temperature mixture. On the contrary, according to the resultof the synthetic resin utilizing the not kneaded polyethylene, signalintensities of the protons of the methyl, methylene and methine radicalscontained in propylene are smaller than those of the room temperaturemixture but resemble to signal intensities manifested by theethylene-propylene block copolymer. Thus, it will be noted thatsynthetic resins prepared in accordance with this example are differentfrom a mere blend of polyethylene and polypropylene.

EXAMPLE 2 In order to determine whether chemical change occurs or not inthe composition when a mixture of a powdery high density polyethyleneresin not kneaded after polymerization and a vinyl polymerization typeresin is heat kneaded in the presence of a radical forming catalyst, apowdery high density polyethylene resin having a melt index of 0.3 (ASTMD-l238) and a melt viscosity of 220,000 poise at a temperature of 190Cand under a rate of shear at 30 see. (an ethylenebutene copolymer andincorporated with 0.05 part of ionol antioxidant), and a polystyreneresin having a rate of shear of 3.5 (ASTM D-l238) and a melt viscosityof 160,000 poise at a temperature of 190C and under a rate of shear at30 see. were admixed at room temperature and at a weight ratio of 20.0.25 part of 2,2-azobisiso butyronitrile acting as the radical formingcatalyst was incorporated into the mixture and the resulting mixture wassubjected to heat kneading treatment which was conducted in a ventedextruder provided with a nylon screw, 40 mm diameter and 1120 mmeffective length. I-Ieat kneading conditions were: the resin temperatureat the die was 240C, the resin pressure at the discharge end of thescrew was kg/cm and the number of revolutions of the screw was 27 rpm.NMR spectra were detennined by means of a nuclear magnetic resonancedevice operating at 60 MHz on the synthetic resin prepared as abovedescribed and on a room temperature mixture consisting of the same typehigh density polyethylene resin once heat kneaded after polymerizationand the same type polystyrene resin at a weight ratio of 80 20. Againhydrogen protons were used as the nuclei, purified tetrachloride as thesolvent. Measuring temperature was 125C for both samples, while theconcentration of each sample was 6.0 percent, all other measuringconditions were maintained constant. FIG. 5 shows the NMR spectrum ofthe room temperature mixture while FIG. 6 shows that of the syntheticresin prepared according to the method of this invention. According tothe result of the synthetic resin of this example, the signalintensities of protons of the phenyl, methylene and methine radicals(represented by a, b and c respectively in FIG. 5 and 6) contained inthe stylene composition are smaller than those of the room temperaturemixture. From this it is evident that the synthetic resins preparedaccording to the method of this example are different from a mere blendof polyethylene and polystyrene.

EXAMPLE 3 Again, in order to determine whether chemical change occurs ornot in the composition when a mixture consisting of a powdery highdensity polyethylene resin not heat kneaded after polymerization and avinyl polymerization type resin is heat kneaded in the presence of aradical forming catalyst, a powdery high density polyethylene resinhaving a melt index of 0.3 (ASTM D-I 238) and a melt viscosity of220,000 poise at a temperature of C and under a rate of shear at 30 sec.(an ethylene-butene copolymer and incorporated with 0.05 part of ionolantioxidant) and a polyvinyl chloride resin having an average degree ofpolymerization of 800 and a melt viscosity of 330,000 poise at atemperature of 190C and under a rate of shear at 30 see. were admixed atroom temperature at a weight ratio of 80 20. 0.05 part of 2,2-azobisisobutyronitrile acting as the radical forming catalyst was incorporated tothe mixture and the resultant mixture was heat kneaded with a ventedextruder provided with a nylon screw having a diameter of 40 mm and aneffective length of 1,120 mm. The conditions of heat kneading treatmentwere: the resin temperature at the die portion was 200C, the resinpressure at the discharge end of the screw was 220 kg/cm and the numberof revolutions of the screw was 29 rpm. NMR spectra were determined bymeans of a nuclear magnetic resonance device operating at 60 MHz on thesynthetic resin prepared as above described and on a room temperaturemixture consisting of the same type high density polyethylene resin onceheat kneaded after polymerization and the same type polyvinyl chlorideresin at a weight ratio of 80 20. Hydrogen protons were used as thenuclei, purified orthodichlorobenzene as the solvent. Measuringtemperature was 140C for both samples while the concentration of eachsample was 6.0 percent. All other measuring conditions were maintainedconstant. FIG. 7 shows the MNR spectrum of the room temperature mixturewhereas FIG. 8 that of the synthetic resin prepared in accordance wihthe method of this example. According to the result of the syntheticresin of this example, the signal intensites of protons of the methyleneand methine radicals (represented by b and c respectively in FIGS. 7 and8) contained in the vinyl chloride component are smaller than those ofthe room temperature mixture. Thus, it is clear that the synthetic resinprepared by the method of this example is different from a mere blend ofpolyethylene and polyvinyl chloride.

EXAMPLE 4 In order to determine whether a chemical change occurs or notin the composition when a mixture of a powdery high density polyethyleneresin not kneaded after polymerization and a vinyl polymerization typeresin is heat kneaded in the presence of a radical forming catalyst,powdery high density polyethylene resins not kneaded afterpolymerization and respectively having melt indices of 0.3, 0.6 and 1.0(ASTM D-l238) and melt viscosities of 220,000, 180,000 and 120,000,respectively, at a temperature of 190C and under a rate of shear at 30sec. (homopolymer and copolymers with butene and incorporated with 0.05part of ionol antioxidant), were respectively mixed with a polystyreneresin having a flow rate of 3.5 (ASTM D-l238) and a melt viscosity of160,000 poise at a temperature of 190C and under a rate of shear at 30sec. at room temperature and at a weight ratio of 90 10 and 80 20. 0.25part of 2,2-azobisisobutyronitrile acting as the radical formingcatalyst was incorporated into the mixtures and the resulting mixtureswere heat kneaded. The apparatus and conditions of kneading employed inthe heat kneading treatment were the same as in example 2. Forcomparison, the same high density polyethylene resin once kneaded afterpolymerization and the same type polystyrene resin were admixed atweight ratios of 90 10 and 80 20 respectively and 0.25 part of2,2-azobisisobutyronitrile was incorporated to respective mixtures.These mixtures were heat kneaded with the same extruder and under thesame conditions of extrusion as the case described above. These samples,the same type high density polyethylene resin, and polystyrene resin(each kneaded after incorporation of 0.25 part of 2,2-azobisisobutyronitrile) were pulverized to have a mean grain size of 250p. and extraction test was carried out for each sample. Purified benzenewas used as the sol vent. For extraction, each sample of about 5.0 g.was immersed in the solvent of 500 ml and let stantstill for days atroom temperature, and the results of extraction are tabulated in table4.

Table 4 High density polyethylene resin 0.8 0.5 90/10 3.6 9.7 /20 10.018.6 Polystyrene resin 99.1 99.1 High density polyethylene resin 0.5 0.6/10 1.2 8.8 80/20 8.5 18.2 Polystyrene resin 99.1 99.1 High densitypolyethylene resin 0.4 0.1 90/ 10 2.6 8.1 80/20 9.2 17.3 Polystyreneresin 99.] 99.1

"': Melt index 0.3, ethylene-butene copolymer. Melt index 0.8,ethylene-butene copolymer. Melt index 0.6, homopolymer.

A: Percentage of extraction nfu kneaded mixture of a high densitypolyethylene not heat kneaded after polymerization and polystyrene.

B: Percentage of extraction of a kneaded mixture of a high densitypolyethylene and polystyrene once heat kneaded after polymerization.

EXAMPLE 5 Again in order to determine whether a chemical change occursor not in the composition when a mixture of a powdery high densitypolyethylene resin not kneaded after polymerization and a vinylpolymerization type resin is heat kneaded in the presence of a radicalforming catalyst, various powdery high density polyethylene resins notkneaded after polymerization and having melt indices of 0.3, 0.6 and1.0, respectively (ASTM D-1238) and melt viscosities of 220,000, 180,000and 120,000 poise, respectively, at a temperature of C and under a rateof shear at 30 sec. (homopolymer and copolymers with butene and eachincorporated with 0.05 part of ionol antioxidant) and a polyvinylchloride having an average degree of polymerization of 800, and a meltviscosity of 330,000 poise at a temperature of 190C and under a rate ofshear at 30 sec. were admixed at room temperature and at weight ratiosof 90 10 80 20 respectively. 0.5

conditions as in the case described hereinabove. These samples, andsamples of the same type high density polyethylene resins, polyvinylchloride resin, each incorporated with 0.50 part of2,2-azobisisobutyronitri1e, were pulverized to have an average grainsize of 250 ,u. and extraction test was carried out for each sample.Purified tetrahydrofuran was used as the solvent. For extraction, eachsample weighing about 5.0 g. was immersed in the solvent of 500 ml, andwas let standstill for 15 days at room temperature. The results ofextraction are shown in table 5.

' Melt index 0.3, ethylene-butene copolymer.

2 Melt index 0.8. ethylene-butene copolymer.

Melt index 0.6. homopolymer. A: Percentage of extraction of a kneadedmixture, of a high density polyethylene not heat kneaded afterpolymerization. B: Percentage of extraction of a kneaded mixture of ahigh density polyethylene once heat kneaded after polymerization and apolyvinyl chloride.

It is evident from table 5 that the percentage of extraction of theresin of this example is lower than that of a mixture consisting of akneaded high density polyethylene and polyvinyl chloride and kneaded byan extruder which shows that the synthetic resin is different from amere blend of polyethylene and polyvinyl chloride.

Above examples are shown to show the advantage of utilizing apolyethylene resin not kneaded after polymerization when preparing blockor graft copolymers with vinyl polymerization type resins.

Following examples illustrate preferred embodiments of this invention.

EXAMPLE 6 A powdery high density polyethylene resin not kneaded afterpolymerization and having a melt index of 0.6 (ASTM D-l238) and a meltviscosity of 180,000 poise at a temperature of 190C and under a rate ofshear at 30 sec. and a saponified ethylene-vinyl acetate co polymercontaining 40.1 mol percent of ethyleneand having a degree ofsaponification of 99.1 percent, such as U.S. Pat. No. 3,419,654, a meltviscosity of 170,000 poise at a temperature of 190C and a rate of shearat 30 sec. were admixed at room temperature and at weight ratios of 95 5and 90 10 respectively. After incorporated with 0.20 part of 2,2-azobisisobutyronitrile acting as the radical forming catalyst, themixtures were heat kneaded with a vented extruder provided with aDulmage type screw having a diameter of 40 mm and an effective length of1,120

mm. The kneading conditions were: the resin temperature at the dieportion was 205C, the resin pressure at the discharge end of the screwwas 335 kg/cm and the number of revolutions was 45 rpm. The syntheticresin- 12 ous composition kneaded in the above described manner wasshaped into films having a mean thickness of 230 microns by T-die methodand the measured values of the moisture permeability A of these (115 Z0208) are shown in table 6 Table 6 HDPE) saponified ethylene-vinylacetate copolymer A *fMelt index: 0.6 homopolymer.

Table 6 shows that films of the novel resinous compositions have muchlower moisture permeability than those of the same type high densitypolyethylene resin 1 along (4.1 g/m 'day-50 p.) and of the same typesaponified ethylene-vinyl acetate copolymer (21.0 g/m 'day'50 p.)prepared by the same machine and under the same conditions as abovedescribed.

EXAMPLE 7 A powdery high density polyethylene resin not kneaded afterpolymerization having a melt index of 0.8 (ASTM D1238) and a meltviscosity of 180,000 poise at a temperature of 190C and under a rate ofshear of 30 sec. and a saponified ethylene-vinyl acetate copolymercontaining 40.1 mol percent of ethylene and having a degree ofsaponification of 99.1 percent, a melt viscosity of 170,000 poise at atemperature of 190C and under a rate of shear at 30 sec. were admixed atroom temperature and at weight ratios of 5 and 90 10 respectively. 0.25part of 2,2- azobisisobutyronitrile serving as the radical formingcatalyst was added to the mixtures and the resulting mixtures were heatkneaded with a vented extruder provided with a Dulmage type screw, 40 mmdiameter Table 7 HDPE saponified ethylene-vinyl acetate copolymer A*Melt index: 0.8. ethylene-butene copolymer.

As can be clearly noted from table 7, the moisture permeability of thefilms of the novel resinous composition is much smaller than those ofthe same type high density polyethylene resin alone (3.5 g/m -day50 p.)and of the same type saponified ethylene-vinyl acetate copolymer alone(21.0 g/m 'day-50 [.L).

EXAMPLE 8 A powdery high density polyethylene resin not kneaded afterpolymerization having a melt index of 0.07 (ASTM D-l238) and a meltviscosity of 510,000 poise at a temperature of 190C and under a rate ofshear at 30 sec. and a saponified ethylene-vinyl acetate copolymercontaining 40.1 mol percent of ethylene and having a degree ofsaponification of 99.l percent, and a melt viscosity of 170,000 poise ata temperature of 190C and under a rate of shear at 30 sec. were admixedat room temperature at weight ratios of 95 and 90 10, respectively.After incorporated with 0.60 part of 2.2-azobisisobutyronitrile actingas the radical forming catalyst the mixture was heat kneaded with avented extruder provided with a Dulmage type screw, 40 mm diameter and1,120 mm effective length. The kneading conditions were; the resintemperature at the die portion was 200C, the resin pressure at thedischarge end of the screw was 470 kg/cm and the number of revolutionsof the screw was 45 rpm. The kneaded resinous composition was shapedinto thin films having an average thickness of 250 microns by T-diemethod and the measured values of the moisture permeability A of thesesheets (JIS Z 0208) are shown in table 8.

"Melt index: 0.07, homopolymer.

As can be clearly noted from table 8, the moisture permeability of thefilms of the novel resinous composi- .g/m 'day'50 p.) and of the sametype saponified ethylene-vinyl acetate copolymer (21.0 g/m -day-50 ,u).

What is claimed is:

1. A block-graft copolymer of polyethylene and saponified ethylene-vinylacetate copolymer which is formed by heating to an elevated temperaturea mixture of polyethylene having a melt index of 0.6 to 0.8 and asaponified ethylene-vinyl acetate copolymer which has a degree ofsaponification of 99 percent or more and kneading the mixture in thepresence of 0.2 to 0.6 parts by weight based on the weight of saidmixture of a radical forming catalysts, said mixture being heated to atemperature from 200 to 205C and kneaded under a pressure of 330 to 470kg/cm said saponified ethylene-vinyl acetate copolymer consisting offrom 30 to 50 mol percent of ethylene, the remainder being vinylacetate, said polyethylene being a powdery, high density polyethylenewhich has not been subjected to heating and kneading afterpolymerization, said mixture containing said high density polyethyleneand said saponified ethylene-vinyl acetate copolymer at a weight ratioof 98:2 to :20.

2. The copolymer according to claim 1 wherein the ratio of said highdensity polyethylene and said saponified ethylene-vinyl acetatecopolymer ranges from 95 :5 to :10 by weight.

3. The copolymer according to claim 1 wherein said radical formingcatalyst is 2,2- azoisobisisobutyronitrile.

2. The copolymer according to claim 1 wherein the ratio of said highdensity polyethylene and said saponified ethylene-vinyl acetatecopolymer ranges from 95:5 to 90:10 by weight.
 3. The copolymeraccording to claim 1 wherein said radical forming catalyst is2,2''-azoisobisisobutyronitrile.